1. Field of the Invention
The present invention relates to a conductive coating composition, which can be coated on a substrate to enable the surface of the substrate to have an electromagnetic wave shielding effect. The present invention also relates to a conductive film formed by the conductive coating composition.
2. Description of the Prior Art
In operation of an electronic device, a certain degree of electromagnetic field is generated, and electromagnetic fields generated by devices may interfere with each other or block each other, or normal operation of neighboring devices is affected. Therefore, if the electromagnetic fields generated by a circuit current are not shielded appropriately, the electromagnetic fields may interfere with each other, and is the quality of signal transmission is deteriorated, so that the devices cannot be operated normally.
As a manner for electronic devices to resist electromagnetic interference, an electromagnetic interference (EMI) shielding material is used as a shielding cover for resisting the electromagnetic interference. The principle of the electromagnetic interference shielding is to adopt a low-resistance (surface resistivity lower than 105 Ω/sq) conductive material, because the conductive material has a reflection and guiding effect on electromagnetic waves. According to the theory of electromagnetic wave shielding of metal materials, the electromagnetic shielding effect of the metal material is the sum of the reflection loss of the electromagnetic wave, the absorption loss of the electromagnetic wave and the loss of the electromagnetic wave in the shielding material.
Most commonly, a complete metal protection net formed by a conductive tape or conductive gasket is adopted, so that the electronic circuit is in a completely isolated space without being interfered by external electromagnetic waves or interfering with other electronic components. The commercially available products include: an aluminum tape, a copper foil tape, an EMI conductive tape, an EMI gasket, a becu finger, a double-sided tape and so on, and moreover, the products have the advantages of simple operation and being easy to be torn and pasted, and are widely used in LCD TVs, laptops, mobile phones, computers and so on.
In the field of touch displays, in order to avoid influence on the normal display function caused by mutual interference between electromagnetic fields of the display and the touch panel, an electromagnetic wave shielding material is generally added between the display and the touch panel. As shown in a schematic view in FIG. 1, a touch display generally includes a touch panel (10), an electromagnetic interference shielding material (11) and a display (12), where the electromagnetic interference shielding material is located between the touch panel and the display. Because the touch panel is disposed in front of the display, the electromagnetic wave shielding material needs to have a high total light transmittance. In the art, indium tin oxide (ITO) is usually used as an electromagnetic interference shielding material, which is a transparent conductive material. However, this material is expensive, and needs to be fabricated through sputtering or deposition in vacuum, resulting in a high production cost. In addition, the ITO material is not flexible, so the application in some electronic products is limited.
Taiwan Patent No. 1353471 discloses that a metal net is used as an electromagnetic interference shielding material for a touch display, and the metal net is fabricated by weaving metal wires having a width that does not influence the vision of naked eyes and having the electromagnetic shielding effect. However, this material needs to be prepared through a photolithography process, and the process is expensive.
In addition, in Taiwan Patent Publication No. TW 201035996, a carbon nanotube is used as an electromagnetic interference shielding material of a touch display. However, synthesis of the carbon nanotube is complex, and the cost is high. Further, the carbon nanotube has a black appearance, and cannot be coated on the whole surface without influence on the light transmittance, so the electromagnetic shielding effect is limited.
Therefore, it is an object expected by the industry nowadays to find a flexible and chemical-resistant transparent material that can effectively isolate electromagnetic waves, has a low cost, and can be applied to various electronic products.